Thermoadhesive conjugate fibers having conjugate form comprising on the fiber surface a low-melting-point component made of polyethylene, a ethylene-propylene-butene copolymer or crystalline polypropylene, and at the fiber center a high-melting-point component made of an ethylene-propylene-butene copolymer, crystalline polypropylene or a polyester, are widely known.
Such thermoadhesive conjugate fibers are usually formed into a web and then heated at a temperature above the melting point of the low-melting-point component and below the melting point of the high-melting point component to allow formation of a nonwoven fabric wherein the contacting sections between the fibers composing the web are fused together.
However, because such thermoadhesive conjugate fibers have low adhesion for other materials (for example, cloth, wood or metal), it is necessary to use a binder (for example, polyvinyl alcohol or the like) to improve the adhesion when the nonwoven fabric is to be employed for obtaining a conjugate material bonded to another material or for blending with other materials to obtain cellulosic fiber blended nonwoven fabrics. When such a binder is used, however, the (cellulosic fiber blended) nonwoven fabric surface becomes coated with the binder to form a film, and this has caused problems such as reduced performance (absorption properties, etc.) of the (cellulosic fiber blended) nonwoven fabric, or in the case of a thick (cellulosic fiber blended) nonwoven fabric, seepage of the binder into the interior resulting in interlayer peeling of the (cellulosic fiber blended) nonwoven fabric.
In recent years, several processes have been developed for the purpose of improving the adhesion in order to overcome these problems (Japanese Patent Application Laid-Open No. 53-126320, Japanese Patent Application Laid-Open No. 54-30929, Japanese Patent Application Laid-Open No. 2000-212866, U.S. Pat. Nos. 4,950,541, 5,981,410). However, it is currently the situation that all of these processes still produce inadequate fiber strength or nonwoven fabric strength, despite providing satisfactory adhesion with other materials.